Clusters
Clustered systems have provided a highly available and highly scalable solution since
initially appearing in the 1980s in the DEC VAXcluster configuration. Clusters can
combine all the components of separate machines, including CPUs, memory, and I/O
subsystems, into a single hardware entity. However, clusters are typically built by
using shared disks linked to multiple ???nodes??? (computer systems). A high-speed interconnect
between systems provides a means of exchanging data and instructions
without writing to disk (see Figure 12-3). Each system runs its own copy of an operating
system and Oracle instance. Grids, described later in this chapter, are typically
made up of a few very large clusters.
Figure 12-3. Typical cluster (two systems shown)
Network Connection
Disk Cabling
CPU with L1 Cache
L2 Cache
Memory
I/O
Disk
CPU with L1 Cache
L2 Cache
Memory
I/O
Disk
296 | Chapter 12: Oracle and Hardware Architecture
Oracle??™s support for clusters dates back to the VAXcluster. Oracle provided a sophisticated
locking model so that the multiple nodes could access the shared data on the
disks.
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